1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to a solid state image sensor and a method of manufacturing the same.
2. Description of the Related Art
Solid state image sensors are used in a variety of applications in disciplines such as public security, industry, broadcasting, and the military. For example, solid state image sensors are used in various devices such as cameras, camcorders, multimedia devices, and surveillance cameras. Particularly, as miniaturization and the number of pixels of solid state image sensors increase, the demand for efficient manufacture of low-cost solid state image sensors, especially those that include on-chip micro-lenses, also increases.
Sensitivity and manufacturing yield are very important details to consider when manufacturing a solid state image sensor. Therefore, micro-lenses are formed on the upper portion of a sensor to improve sensitivity. A light ray incident on the solid state image sensor passes through the micro-lens, which is installed for improving the light collection efficiency, and the light energy is collected by a photodiode. The light energy collected by the photodiode is converted into a signal charge, and the signal charge is transmitted to an output terminal by a transmission device such as a vertical transmission charge-coupled device (CCD) or a horizontal transmission CCD. The signal charge transmitted to the output terminal is output as an electrical signal corresponding to the amount of energy imparted by the incident photons.
FIG. 1 is a sectional view illustrating a solid state image sensor including conventional micro-lenses.
Referring to FIG. 1, micro-lenses 122 are formed on a flat protection layer 120. The micro-lenses 122 are generally formed of an organic substance including photoresist. Photoresist patterns are formed, and are then heat treated and flowed, thereby forming convex lenses having a proper radius of curvature. However, if the photoresist patterns are formed by a thermal flow in two-dimensions on a flat protection layer 120, the radius of curvature of the respective micro-lenses 122 can vary, due to variations in local surface energy over a large area. Also, when forming the micro-lenses 122, thermal energy is continuously applied. If the contact area between the micro-lenses and the protection layer is large, that is, the radius of curvature is large, some micro-lenses may be stuck to an adjacent micro-lens, while other micro-lenses may not be stuck to an adjacent micro-lens. The thickness of the photoresist in the overlapped portions of the micro-lenses stuck to each other may be different. A diffused reflection is caused by excessive overlapping of micro-lenses. Therefore, in the respective micro-lenses, a difference in sensitivity occurs due to a difference in transmitted light intensity, and uniformity in sensitivity is reduced. Therefore, there is an imposed manufacturing limit in the maximum radius of curvature of the micro-lens in order to secure an improvement in sensitivity and a uniformity of size of the micro-lenses.
To address the above limitations, it is a first objective of the present invention to provide a solid state image sensor which can maintain uniformity of the size of the micro-lens and can secure uniformity in sensitivity by forming the radius of curvature of the micro-lens to be as large as possible.
It is a second objective of the present invention to provide a method for manufacturing a solid state image sensor which can maintain uniformity of the size of the micro-lens and can secure uniformity in sensitivity, and can form the radius of curvature of the micro-lens to be as large as possible.
Accordingly, to achieve the first objective, a solid state image sensor includes trapezoidal separated sections of the protection layer which is formed on a predetermined lower layer of a semiconductor substrate, and convex micro-lenses each having a predetermined radius of curvature that are connected to each other by filling separations between trapezoidal separated sections of a protection layer with photoresist.
A flattening layer may be further included between the predetermined lower layer formed on the semiconductor substrate and the protection layer.
A layer of color filters, each filter corresponding to a separated section of the protection layer, may be further included between the flattening layer and the protection layer.
The separations between the separated sections of the protection layer preferably have a structure such that the upper portions are wider than the lower portions.
Points of contact where the upper portions of the micro-lenses connect to each other are formed preferably around the upper portions of the separations.
The predetermined lower layer formed on the semiconductor substrate may be a photodiode, a channel region, an electric charge transmission region, a gate dielectric layer, electric charge transmission electrodes, interdielectric layers, and a shading layer.
It is preferable that the protection layer is formed of a polyimide layer of a polyacryl series of a hybrid type, and that the micro-lenses are formed of a Novolak resin.
To achieve the second objective, there is provided a method for manufacturing a solid state image sensor including the steps of (a) forming trapezoidal separated sections of a protection layer by coating polyimide on a predetermined lower layer of a semiconductor substrate and using photolithography, (b) coating photoresist onto the protection layer and forming photoresist patterns, and (c) flowing the photoresist patterns into the separations between the trapezoidal separated sections of the protection layer by applying thermal energy to the photoresist patterns, and forming the micro-lenses to be connected to each other.
Before the step of forming the protection layer, a step of forming a flattening layer on the semiconductor substrate on which a predetermined lower layer is formed may be further included.
After the step of forming the flattening layer but before the step of forming the protection layer, a step of forming a layer of color filters, in which each filter corresponds to a separated section of the protection layer, may be further included.
In step (c), the photoresist may be flowed in two steps. A first step of flowing the photoresist patterns forms micro-lenses having a first radius of curvature on the separated sections of the protection layer. In a second flowing step, by applying thermal energy, photoresist flows into the separations between the separated sections of the protection layer, thereby forming micro-lenses having a second radius of curvature greater than the first radius of curvature.
It is preferable that points of contact on the upper portions of the micro-lenses connected to each other are proximal to the upper portions of the separations.
It is preferable that the separations between the separated sections of the protection layer have a structure such that the upper portions are wider than the lower portions.
A predetermined lower layer formed on the semiconductor substrate may be a photodiode, a channel region, an electric charge transmission region, a gate dielectric layer, electric charge transmission electrodes, interdielectric layers, and a shading layer.
It is preferable that the protection layer is formed of a polyimide layer of a polyacryl series of a hybrid type, and that the micro-lenses are formed of an organic substance, i.e., a Novolak resin.
In another aspect, the present invention is directed to a solid state image sensor and method. A protection layer is formed on a lower layer of a semiconductor substrate. Partitioning grooves are formed in the protection layer, the grooves defining micro-lens positions. Convex micro-lenses are formed on the protection layer at the micro-lens positions, the micro-lenses being connected to each other at the partitioning grooves, each of the micro-lenses having a radius of curvature.
The grooves preferably are wider at a top portion than at a bottom portion. The upper surfaces of the respective micro-lenses may be coupled to each other in a region proximal to the top portion of the partitioning grooves.
The micro-lens positions are preferably trapezoidal in cross-sectional profile.
A flattening layer may be provided on the lower layer, and a color filter may be provided on the flattening layer.